1. Field of the Invention
The present invention generally relates to a printer and in particular to a control method for print data including binary image data and multilevel image data.
2. Description of the Related Art
There have been proposed image forming apparatuses or printers that can combine binary image data such as text data with multilevel image data such as graphics data to form mixed text-and-graphics output. For example, in Japanese Patent Unexamined Publication No. 8-256255, combining control data is provided for each dot and according to the combining control data the binary image data and the multilevel image data are processed to form the mixed text-and-graphics output.
There are some conventional image forming apparatus or printer having an outline correction or smoothing function. For example, in Japanese Patent Unexamined Publication No. 5-227433, multilevel image data is converted into a dot pattern representing halftone and then each pixel is compared to surrounding pixels of the pixel. If a predetermined pattern is detected in the surrounding pixels, the outline of the dot pattern is corrected according to the predetermined pattern.
However, the conventional printer using combining control data needs an extra memory for storing the combining control data for each dot, resulting in increased memory capacity.
The other conventional printer having the outline correction function performs outline correction regardless of type of print data when the predetermined pattern is detected in the surrounding pixels. In other words, even in the case where print data is in no need of outline correction, the outline correction is performed if the predetermined pattern is detected, resulting in deteriorated image quality.